The present application claims priority to Japanese Patent Application No. 2001-159403, filed May 28, 2001. The contents of that application are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or other similar image forming apparatus.
2. Discussion of the Background
An image forming apparatus such as a copying machine, a printer, a facsimile machine, or other similar image forming apparatus, employs a transfer method in which a visual image, e.g. a toner image, formed on an image carrier such as a photoreceptor is transferred onto a recording material, e.g., a transfer sheet, via an intermediate transfer element. An image forming apparatus using an intermediate transfer element is widely used because of advantages in forming visual images on sheets of various sizes and in numerous layouts of devices in the image forming apparatus.
There are two types of the above-described image forming apparatuses using the intermediate transfer element: (1) an image forming apparatus including a single image carrier and an intermediate transfer element; and (2) an image forming apparatus including a plurality of image carriers and an intermediate transfer element (so-called tandem type image forming apparatus). The tandem type image forming apparatus is mainly used for obtaining a large number of copies or prints.
As an intermediate transfer element in the above-described image forming apparatus, an endless belt including a single layer or plural layers is often used. An intermediate transfer element typically has a volume resistivity from 107 xcfx89cm to 1015 xcfx89cm. A discharging device may be provided to remove a residual charge on the intermediate transfer element if the intermediate transfer element is electrically charged. Further, a cleaning device in a shape of blade or brush is commonly used for removing unnecessary toner remaining on the intermediate transfer element.
Generally, a discharging device for an intermediate transfer element is provided in downstream of a cleaning device in a rotating direction of the intermediate transfer element. For example, Japanese Patent Laid-open Publications No. 6-161298 and No. 2000-56588 describe image forming apparatuses including such discharging devices.
Japanese Patent Laid-open Publication No. 6-161298 describes an image forming apparatus in which a charge on a filming layer in an intermediate transfer element is removed to obtain adequate and stable transfer efficiency for a long period of time. Japanese Patent Laid-open Publication No. 2000-56588 describes an image forming apparatus in which image unevenness is prevented from occurring in an image forming process by uniformly removing a residual charge remaining on an intermediate transfer element.
An image forming apparatus typically has a problem of removed toner attaching back onto an intermediate transfer element. Specifically, residual toner, which has been removed from the intermediate transfer element by a cleaning device, moves back onto the intermediate transfer element from the cleaning device because a charging condition of the residual toner removed by the cleaning device is not controlled. The toner re-attached to the intermediate transfer element remains in a subsequent image forming process and stains a toner image formed on the intermediate transfer element in the subsequent image forming process, resulting in an image deterioration.
According to one aspect of the present invention, an image forming apparatus includes at least one image carrier configured to carry a visual image formed thereon, an intermediate transfer element configured to carry the visual image from the at least one image carrier to a recording material, a primary transfer device configured to transfer the visual image from the at least one image carrier onto the intermediate transfer element, and a secondary transfer device configured to transfer the visual image on the intermediate transfer element onto the recording material, a cleaning device configured to make contact with the intermediate transfer element to mechanically remove developer remaining on the intermediate transfer element, and a discharging device configured to discharge the intermediate transfer element. The discharging device is positioned in downstream of the secondary transfer device and upstream of the cleaning device in a moving direction of the intermediate transfer element.